Human beings are of course unique. They have, perched between their ears, the most complicated biological machine on the planet. But complexity is no… - Matt Ridley

Montagues and Capulets, French and English, Whig and Tory, Airbus and Boeing, Pepsi and Coke, Serb and Muslim, Christian and Saracen – we are irredeemably tribal creatures. The neighbouring or rival group, however defined, is automatically an enemy. Argentinians and Chileans hate each other because there is nobody else nearby to hate.

Jealousy is a “human universal,” and no culture lacks it, Despite the best efforts of anthropologists to find a society with no jealousy and so prove that it is an emotion introduced by pernicious social pressure or pathology, sexual jealousy seems to be an unavoidable part of being a human being.

With increasingly money-based interactions among strangers, people increasingly began to think of neighbours as potential trading partners rather than potential prey. Killing the shopkeeper makes no sense.